Pliny the Younger
Caius Caecilius - the younger Pliny (ad 61 or 62-113) - was born in a Roman high society family in Como. His uncle (his mother’s brother) was Pliny the Elder, a naturalist, natural philosopher, naval and army commander, and friend of the emperor Vespasian.
Pliny the Elder died during the Vesuvius eruption that destroyed Pompeii and Herculaneum in August 79 while he was trying to rescue friends. The younger Pliny was the heir of his uncle and the change of name - Caius Plinius Luci filius Caecilius Secundus - indicates his adoption by will as a son (his father, Lucius Caecilius had died while he was very young). Pliny started his career at the Roman bar at the age of 18. He moved through the regular offices in a senator’s career, even becoming consul in 100 under Emperor Trajan. On this occasion he delivered the speech of thanks known as the Panegyricus. However, he is better known for his letters that are considered to be a social document of his times and are praised for the quality of their prose.The letter that interests us is Letter 14 in Book VIII (Pliny 1969) and was brought to the attention of social choice theorists by Robin Farquharson (1969) in his exceptional book on strategic voting (on Farquharson see Dummett 2005). Farquharson’s book includes a 1752 translation by John, Earl of Orrery, of Pliny’s letter. According to Riker (1986: 88), the translator “did not seem to understand the parliamentary issues involved and therefore did not see what happened at the end of the event”. There is, fortunately, a new translation by Betty Radice in Pliny (1969).
Pliny’s letter is to Titius Aristo, a pre-eminent jurist. After a long digression praising the addressee, Pliny explains that “the case at issue concerned the freedmen of the consul Afranius Dexter, who had been found dead; it was not known whether he had killed himself or his servants were responsible, and, if the latter, whether they acted criminally or in obedience to their master.” Three kinds of decisions were then suggested: acquittal, banishment or death penalty.
(Pliny also suggests that some people were in favour of banishment for the freedmen and death for the slaves, although there is no further mention of slaves.) Pliny wished to have a plurality voting system in this case: “my own proposal was that the three sentences should be reckoned as three, and that two should not join forces under a temporary truce” (Pliny 1969: 39). He feared the formation of a coalition of senators in favour of death with those in favour of banishment, defeating those who were in favour of acquittal. He even imagined a run-off with a vote on death against banishment. Although the letter does not explain this, we can infer from it that the banishment penalty would have defeated both acquittal and death penalty in pairwise majority voting, being what is now called a Condorcet winner. Pliny succeeded in his request to have a (one round) plurality vote. Then:the proposer of the death sentence was convinced by the justice of my request..., dropped his own proposal, and supported that of banishment. He was afraid, no doubt, that if the sentences were taken separately (which seemed likely if he did not act) the acquittal would have a majority, for there were many more people in favour of this than either of the other two proposals. Then, when those who had been influenced by him found themselves abandoned by his crossing the floor and the proposal thrown over by its author, they dropped it too, and deserted after their leader. So the three sentences became two, and the second carried the day by elimination of the third which could not defeat both the others, and therefore chose to submit to one. (Pliny 1969: 45)
It seems clear in Radice’s translation that the senate voted for the banishment penalty. According to Riker (1986) Pliny proposed the plurality rule because he thought that voters would vote sincerely. He tried to manipulate the Roman Senate by promoting a rule that would generate the decision he was in favour of: acquittal. However, he did not understand clearly that those in favour of the death penalty would manipulate the voting rule by voting strategically. The 1752 translation is unclear on this and a French translation by Annette Flaubert (Pliny 2002) has a footnote in which it is said that acquittal carried the day!
It remains that Pliny describes a situation that is manipulable (by a coalition) in the modern sense of Gibbard and Satterthwaite: a group of individuals by voting strategically forces the voting rule to generate an outcome that the members of the group prefer to the outcome that would have prevailed if they had not voted strategically.